Numerical model for separation of H-D gas mixture in batch-type concentric-tube thermal diffusion columns

The modeling simulation for the separation of H-D gas mixture in batch-type concentric-tube thermal diffusion columns have been analyzed from the transport equation coupled with the application of mass balance. The most important assumption is that the concentrations of H₂, HD and D₂ are locally equilibrium at every points in the column as H₂ + D₂ ↔ 2HD. The concentration distribution equation was derived and the concentration difference between the bottom and top ends of the column could be estimated. The degree of separation and separation factor for recovery of deuterium from H-D gas mixture in the batch-type cryogenic-wall thermal diffusion column were estimated.     

The theoretical study of the deuterium enrichment of H-D gas mixture in continuous-type thermal-diffusion columns

The separation equations for enrichment of deuterium in H-D (Hydrogen-Deuterium) gas mixture by continuous-type thermal diffusion columns were developed theoretically. The transport equation modeling treats the enriching and stripping sections separately for each component of H₂-HD-D₂ system to estimate the concentration between the bottom and top ends of the thermal diffusion column. The empirical expressions of the transport coefficients were determined with the previous experimental data (Arita et al., 1998) correlating in the exponential form in terms of operating pressure. The theoretical predictions of the degree of separation and separation factor for recovery of deuterium from H-D gas mixture are in good agreement with the experimental results.     

Recovery of deuterium from H–D gas mixture by thermal diffusion in the Frazier scheme

The separation equation for predicting the deuterium recovery from H–D gas mixture by thermal diffusion in the cocurrent-flow Frazier schemes has been derived. The degrees of separation, as well as separation factors, for deuterium recovery in the Frazier scheme of cryogenic wall thermal-diffusion columns were estimated, with the use of the experimental data obtained by Arita et al. and the transport coefficients correlated in the previous work. Considerable enhancement in deuterium recovery is achievable if the number of thermal diffusion columns in a Frazier scheme is continuously increased, especially for the operation under higher volume flow rate and/or lower operating pressure.     

Recovery of deuterium from H-D gas mixture by thermal diffusion in a multi-concentric-tube column device of fixed total sum of column heights with transverse sampling streams

The effect of the increment in the number of concentric-tube thermal diffusion columns on the recovery of deuterium from H₂-HD-D₂ system with fixed total sum of column heights, has been investigated. The equations for predicting the degrees of separation in single-column, double-column and triple-column devices have been derived. Considerable improvement in recovery can be achieved if a multi-column device with larger number of column is employed, instead of a single-column device with column height equal to the same total sum of column heights, especially for the case of higher flow-rate operation and larger total sum of column heights.     

Separation of deuterium from H-D gas mixture by thermal diffusion in the devices of multi concentric-tube columns with total sum of column heights fixed

The equation for predicting the degrees of separation for deuterium recovery from the H₂-HD-D₂ system using thermal diffusion in single-column, double-column and triple-column devices are derived. The column number effect on separation efficiency with a fixed total sum of column heights is then investigated. Considerable improvement in recovery can be achieved in multi-column devices, instead of a single-column device with the column height equal to the same total sum of column heights, especially for the cases of higher flow-rate operation and larger total sum of column heights.     

Improvement in deuterium recovery from water–isotope mixture by thermal diffusion in the device of branch columns

Deuterium recovery from water–isotopes mixture using thermal diffusion can be improved by employing the branch column device, instead of single column devices, with the same total column length. The remixing effect due to convection currents in a thermal diffusion column for heavy water enrichment is thus reduced and separation improvement increases when the flow rate or the total column length increases. The improvement in separation can reach about 50% for the numerical example given.     

The best column number in the countercurrent-flow Frazier scheme for deuterium recovery from water-isotopes mixture by thermal diffusion with total sum of column height fixed

The effect of column number on thermal diffusion in the countercurrent-flow Frazier scheme with total sum of column heights (L = Nh) fixed, has been investigated. The equations, which may be employed to predict the proper column number for the best performance are derived. Considerable improvement in performance is obtainable if the scheme is constructed with the proper number of thermal diffusion columns, instead of using a single column with column height L (N = 1, h = L). This is because that increasing the column height in a thermal diffusion column though increases the effective separation section, the increment in performance with the increase of column height will decrease, and finally the separation efficiency reaches a limiting value.     

The optimal column number for the improvement in heavy water removal rate from water-isotopes mixture by thermal diffusion in the countercurrent-flow Frazier scheme with the total sum of column heights fixed

The effect of column number on the enrichment of heavy water from water-isotope mixture in the countercurrent-flow Frazier scheme with total sum of column heights L fixed, has been investigated. The equations, which may be employed to predict the optimal column numbers for maximum performances, have been derived. Considerable improvement in removal rate is obtainable if the scheme is constructed with the optimal column number of thermal diffusion columns, especially for larger flow rate with smaller L, or smaller flow rate with larger L.     

Optimal plate aspect ratio for the enrichment of heavy water from water-isotope mixture in a flat-plate thermal diffusion column with transverse sampling streams

Suitably adjusting the plate aspect ratio in a flat-plate thermal diffusion column is one of the flexible ways of properly controlling the convective strength, resulting in reducing the remixing effect while still preserving the effectively cascading effect, and thereby leading to improved separation.The optimal plate aspect ratios for the performances of the separation of heavy water from water-isotope mixture in flat-plate thermal diffusion columns with transverse sampling streams have been determined. The maximum separation and maximum production rate are achieved without changing the total expenditure, while the design with minimum plate surface area results in minimizing the total expenditure.     

Theory of recovery of deuterium from water–isotopes mixture in spiral wired thermal diffusion columns of the Frazier scheme

A separation theory for the recovery of deuterium from water–isotopes mixture in the Frazier scheme of concentric-tube thermal diffusion columns with a tight fitting wire spiral, having a diameter equal to the annular spacing, wrapped on the entire inner tube, has been developed. Equations of the optimal wire angle of inclination for maximum separation, maximum production rate and minimum column height have been derived. Considerable improvement in performance is obtainable if the wire spiral is employed in the column at the optimum inclined wire-angle, instead of the absence of wire spiral, so that the convection strength can be properly reduced and controlled, resulting in suppression of the undesirable remixing effect while still preserving the desirable cascading effect.